This application claims the priority of German Application No. 196 24 043.3, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a measuring process as known from U.S. Pat. No. 4,026,654. In the case of the known process, two measuring devices are provided which are completely independent of one another and may operate, for example, on a different basis. Thus, the measuring device for a short distance range may operate on an ultrasound basis and the measuring device for a longer distance range may operate on a radar or laser basis.
There is therefore needed a simplified measuring process of the above-mentioned type to the extent that the measuring equipment required for this purpose is simplified.
These needs are met according to the present invention by process for measuring the distance between a motor vehicle and an object, in which, in the vehicle, in the case of a short distance to the object, the output signals of a first measuring device with a corresponding measuring range and, in the case of a longer distance to the object, the output signals of a second measuring device with a corresponding larger measuring range are taken into account in a dominating manner. The measuring devices are constructed as analysis devices. The output signal of a single receiver for a single distance generator is fed to the analysis devices as an input signal. The analysis devices analyze this input signal via an analysis process characteristic of the short distance range or of the long distance range.
According to the present invention, only a single sensor is required which scans the whole distance range. The sensor can operate on a laser or radar basis. The use of ultrasound should, as a rule, be eliminated when a distance range is involved which on the whole is relatively long and measures more than ten meters.
The sensor emits a test signal, preferably a periodically repeated frequency-modulated continuous wave radar signal (FMCW). The signals reflected by an object are received by a single receiver and fed to the two analysis devices. There, the input signal is treated by means of analyzing processes which are characteristic of the respective distance range.
The output signal of the two analysis devices is weighted differently corresponding to the respective distance of the measuring range.
The analysis processes for the respective measuring ranges can have different designs. Having a particularly good resolution precision, a correlation process is suitable for the short distance range. In this case, the reflected signal is correlated with a reference signal; for example, is subjected to an auto correlation and the distance of the respective object is determined in this manner. Alternatively, the analysis process can be a spectral analysis process according to a Fast Fourier Transform (FFT) process using a signal delay line.
For the longer distance range, different measuring processes are also known. In tests, the use of a spectral analysis was found to be particularly advantageous. In this case, a radar signal is modulated in the transmission frequency in a suitable manner, for example, in a saw tooth shape or a triangular shape and, from the frequency shift, the distance is determined by means of a spectral analysis. It is also possible to determine the distance by the transit time of a radar pulse which is frequency-modulated during its emission.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.